Having trouble with EF Core / ASP.NET Core MVC MultiSelectList selectedItems

Question

I am trying to set up a multiselect list so that I can assign multiple modules to a company. When I create a new company and assign modules, it works correctly. But when I go to edit a company I cannot figure out why the pre-selected modules will not show.

When I debug I can see that it's passing the correct data for both the company and the list of modules but the pre-selected options don't show on the edit page. The selecteditems should be a list, correct?

Any help would be appreciated.

public class Company
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class SiteModules
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class CompanySiteModules
{
    public int CompanyId { get; set; }
    public Company Company { get; set; }
    public int SiteModuleId { get; set; }
    public SiteModule SiteModule { get; set; }
}

In my repository:

public async Task<Company?> GetCompanyById(int id)
{
    return await context.Companies
                        .Include(x => x.SiteModules)
                        .Include(y => y.CompanyType)
                        .FirstOrDefaultAsync(x => x.Id == id);
}

public async Task<List<int>> GetAllMods(int id)
{
    var modules = await context.CompanySiteModules
                               .Where(x => x.CompanyId == id)
                               .ToListAsync();
    var modulesList = modules.Select(t => t.SiteModuleId).ToList();

    return modulesList;
}

In my controller:

var company = await companyRepository.GetCompanyById(id);
var selectedModules = await companyRepository.GetAllMods(id);

SiteModulesList = new MultiSelectList(context.SiteModules, "Id", "Name", selectedModules)

My page:

<label class="form-label">Modules</label>

<select class="form-select" 
        asp-items="@Model.SiteModulesList" 
        asp-for="SiteModulesList"></select>